Containers holding liquids or other products are designed to accommodate for changes in internal pressure created during packaging or subsequent handling.
For example, hot-filled plastic containers are used for packaging certain liquids, which must be filled into the container while hot. During filling, the product is typically dispensed into the container at elevated temperatures of at least about 82 degrees Celsius. The container is then capped and, as the product cools, a negative internal pressure forms within the sealed container. Improper design may lead to deformation resulting in poor aesthetics, performance and end-user handling. Hot-filled plastic containers are typically blow molded from polyester resin and other suitable polymeric materials, such as biaxially-oriented polyethylene terephthalate (PET), and having a base, a generally cylindrical body, a shoulder, and a neck.
Internal negative pressure may also be created when a packaged product is placed in a cooler environment, e.g., placing a bottle in a refrigerator or a freezer.
To accommodate the shrinkage and negative internal pressure that develops during packaging or subsequent handling, it is known to incorporate a plurality of recessed vacuum panels into the body portion of the container. As the product cools, the vacuum panels will deform and move inwardly thereby relieving internal pressure. Labels may be used around the bell-shaped shoulder portion or to cover the vacuum panels to improve the appearance of the container.
The design of vacuum panels may vary. For example, WO 00/50309, Melrose, discloses a container comprising controlled deflection flex panels having initiator portions that may invert and flex under pressure to avoid deformation and permanent buckling. U.S. Pat. No. 5,971,184, Krishnakumar et al., discloses containers comprising only two vacuum panels and two reinforcing sections (finger grip portions). U.S. Pat. No. 6,837,390, Lane et al., discloses a container comprising a pair of opposing panels and a pair of opposing columns and forming a substantially oval cross section, wherein the columns deflect outwardly as the vacuum panels deflect inwardly. U.S. Pat. No. 6,044,996, Carew, et al., requires an odd number vacuum panels, e.g., five or seven. All references are hereby incorporated by reference.
However, standard six panel designs present difficulties with labeling and end-user handling, and two panel designs show tendency to pull on the columns or grip areas during the optimization to increase volume contraction and reduce pressure. This may contribute to unnecessary distortion on the rigid columns or grip areas and/or on the vacuum panels. Also, the substantially oval shape of these designs often leads to distortion of the shoulder and/or bottom portions of the container, thereby distorting around labels.